Puberty in young Chianina x Brahman and Brahman bulls

Eleven F1 Chianina x Brahman (Ch x Br), and nine Brahman (Br) bulls were used to study puberty according to Wolf's definition. They were kept together under the same environmental and management conditions from 7 to 24 months of age. Monthly measures of age (AG), body weight (BW), scrotal circumference (SC), spermatic concentration (EC), and individual spermatic motility (IM) were taken. Trait relationships were established through estimation of pair-wise correlation, and polynomial regression. Mean values at puberty were for AG=16.3+/-3.9 and 18.1+/-0.9 months, for BW=331+/-90 and 302+/-42 kg; for SC=26+/-3 and 25+/-2 cm, for EC=77+/-47x10(6) and 75+/-48x10(6) sperm cells / ml and for IM=30+/-23 and 37+/-23% for Ch x Br and Br, respectively. There were no statistical difference between groups (t test) for any variable. Correlation coefficients between AG and BW, AG and SC, and BW and SC were 0.90, 0.78; 0.88, 0.79 y 0.89, 0.90 for Ch x Br and Br, respectively. The following regression equations were proposed: BW = 155.0205 + 0.0148 (AG) + 0.0006(AG)(2), R-2 = 0.83; BW = 203.7106 - 0.2111 (AG) + 0.0007 (AG)(2), R-2 = 0.65; SC = 11.9729 + 0.0277 (AG) + 0.000002 (AG)(2), R-2 = 0.78; SC = 17.9568 - 0.0136 (AG) + 0.00004 (AG)(2), R-2 = 0.66; SC = 2.260 + 0.1040 (BW) - 0.00009 (BW)(2,) R-2 = 0.82 y SC = 7.4856 + 0.0498 (BW) + 0.00001 (BW)(2), R-2 = 0.82 for Ch x Br and Br, respectively. Genotypes performed similarly for trait at the time they reached puberty. Crossbred bulls, however, tended to show greater body and testicular development that Brahman throughout the study.